Horseradish Fungus - Knowledgebase Question

I have a bed of horseradish - Maliner Kren variety - which is very prolific and 4 years old.

Last year I started noticing circular spots on the leaves which look like some kind of fungus that spread and the leaves end up dying. It appears to also go down into the root as when I harvested the root had some soft green sections which looked like rot.

I used a soluble copper based fungicide but that did not stop the spread. Any ideas?

There's a disease call White Rust that can attack horseradish (and radish). This fungal disease affects both leaves and roots, and can overwinter in the soil. Many weeds are also hosts, so removing the affected horseradish plants and cleaning up weed debris will go a long way in helping you control the disease. The fungal spores are spread by wind and often infect leaves when air temperatures are 68F and free water is present. Fungicides are not very effective in the control of White Rust.

I'd plant horseradish in a different part of the garden, and use new plants or fresh seeds, to avoid carrying the disease to the new plot.